1. Field of the Invention
This invention relates to a polymethylsiloxane which contains silicon-bonded hydrogen atoms and exhibits low temperature properties (ca. -120.degree. C.), i.e. does not crystallize at low temperatures. This invention also relates to compositions made from this polymethylsiloxane which contains silicon-bonded hydrogen atoms, such as by adding a crosslinking agent. The compositions can also exhibit the low temperature properties.
2. Background Information
The need for materials which exhibits low temperature properties continues to exist because more applications for such materials are being found. Many applications are found in aerospace equipment and uses in the arctic regions. Fluids and cured materials which will not change properties when exposed to low temperatures, such as -120.degree. C., find utility in many places. Low temperature silicones gels, for example, are described by Brown et al. in U.S. Pat. No. 4,374,967, issued Feb. 22, 1983. These silicone gels find use as dielectric silicone gels. Brown et al. teach that their gels can be made by using a special vinyl containing polyorganosiloxane which contains dimethylsiloxane units, methylsilsesquioxane units, trimethylsiloxy units, and monovinyldimethylsiloxy units to obtain the low temperature properties. Brown et al. prefers to crosslink the gel with a polyorganosiloxane which has two silicon-bonded hydrogen atoms per molecule, and these hydrogen atoms are preferably on the ends of the linear polymer.
Polymethylsiloxanes containing silicon-bonded hydrogen atoms which also exhibit low temperature properties are not known to the inventors. Polmanteer et al. in U.S. Pat. No. 3,697,473, issued October 10, 1972, teach many types of polyorganosiloxanes which contain silicon-bonded hydrogen atoms but do not teach any class of such polyorganosiloxanes which exhibit low temperature properties. Polmanteer et al. at column 5, lines 28 to 30, teach a copolymer containing three to ten units of R.sub.2 'HSiO.sub.0.5 and the remaining units being R.sub.2 'SiO.sub.2, R.sub.2 'SiO.sub.1.5, and R.sub.2 'SiO.sub.0.5 in which R' is an alkyl radical having from 1 to 12 carbon atoms, phenyl, or 3,3,3-trifluoropropyl. Polmanteer et al. do not teach any low temperature properties but are interested in obtaining high strength properties.